by Jeff Schaeffer · July 1, 2015
Many inland fisheries historically have allowed unlimited harvest of panfish, or have extremely liberal bag limits. The management paradigm is that fishing mortality is usually low and high harvests benefit angling by improving growth and preventing stunting. However, a new study by Andrew Rypel of the Wisconsin Department of Natural Resources, Bureau of Science Services, shows that this may not be a universal truth and that bag limits can be used to improve fishing quality.
Rypel evaluated a series of lakes with control (25-fish aggregate bag limit) and experimental treatments that reduced the aggregate bag limit to 10 fish. Mean total length increased by about 20 mm in treatment lakes, although the effect varied with Secchi depth; lower water clarity conferred a greater increase, presumably because lakes with lower water clarity were more productive and Bluegills Lepomis macrochirus also grew faster. The effects were also striking in that the experiment ran for three years, and Wisconsin Bluegills routinely achieved age-10. Thus, the regulation covered only 20-30% of the lifespan of individuals in the population. Rypel notes that, although effects were positive, benefits via size structure change might take several years to accrue because of the regulation-lifespan difference. And although few creel data were available to examine angling impacts, experimental lakes developed local reputations for quality Bluegill fishing.
But perhaps the most insightful part of the study was the suggestion that managers need to carefully plan for success in situations where regulation changes may require years to achieve success. Rypel’s thoughtful analysis of this problem discusses a broad range of long-term considerations that apply to managers considering any type of long-term management strategy
Rypel, A. L. 2015. Effects of a reduced daily bag limit on Bluegill size structure in Wisconsin lakes. North American Journal of Fisheries Management 35:388-397. dx.doi.org/10.1080/02755947.2014.1001929